Disposable capillary reservoir pen for graphical recorder

ABSTRACT

The pen for a graphical recorder contains ink in a sinuous capillary path having a predetermined hydraulic diameter. One embodiment of the pen includes priming means integral therewith.

United States Patent [191 Siden DISPOSABLE CAPlLLARY-RESERVOIR PEN FORGRAPHICAL RECORDER [76] Inventor: Terry C. Slden, 708 Park FL, Apt. 4,

Escondido, Calif. 92025 [22] Filed: June 7, 1971 21 Appl. No.: 150,468

[52] U.S. Cl 346/140, 401/192, 401/240 [51] Int. Cl. Gold 15/16 [58]Field of Search, 346/140; 401/192,

[5 6] References Cited UNITED STATES PATENTS 2,678,633 5/1654 .Holden'et a1; 401/192 [in 3,747,121 1451 July17,1973

3,120,214 2/1964 Stegenga 346/140 3,482,257 12/1969 Bowditch et a1...346/140 3,140,912 7/1964 Davis et a1. 346/140 Primary Examiner-Joseph'W. Hartary Attorney-Stephen P. Fox

[57 1 ABSTRACT The pen for a graphical recorder contains ink in 11sinuous capillary path having a predetermined hydraulic diameter. Oneembodiment ofthe pen includes priming means integral therewith.

3 Claims, 7 Drawing Figures PAIENIEB JUL 1 H915 INVENTOR. TERRY c. 51

AT TOQNE Y 3,747,121 1 2 DISPOSABLE CAPILLARY-RESERVOIR PEN FORBACKGROUND OF THE INVENTION EMBODIMENTS Referring now to FIGS. 1-4,there is shown one em- One type of pen used in a graphical recorder suchas bodiment of the pen. A cylindrical outer sleeve 11 suran X-Y plotterincludes a plastic housing having a pen tip on one end and containing alatex sack or bladder filled with ink. This type of pen has severaldisadvantages. For example, the pen is highly susceptible to leakingwith changes in atmospheric temperature and pressure. When the pen isfirst used, or when it is used after a long idle period, it is generallyrequired to use external devices, such as a lever actuated mechanism forcompressing the ink sack to prime the pen to force ink through the pentip. The pen cannot be refilled without disassembling it. This is a timeconsuming operation, since such pens usually comprise on the order ofsix different pieces and require approximately assembly steps. Finally,the level of ink remaining in the pen is usually undetectible until thepen ceases to write in use.

SUMMARY OF THE INVENTION The present invention is a pen having featureswhich obviate the disadvantages described above. The illustratedembodiment of the invention is a transparent plastic structure which isconfigured to define a convolute capillary fluid passageway forcontaining an ink supply. One end of the passageway is coupled to a pentip while the other end is exposed to the atmosphere. The capillarypassageway has predetermined physical parameters which optimize writingspeed and ink drying time. The pen includes a minimum number of partsand is easily assembled to form an integral plastic block. Oneembodiment of the pen includes a deformable cavity integral with the penblock and in communication with the capillary passageway. The cavitywhen manually deformed operates to prime the pen to force ink to flowout of the pen tip.

The advantages of the pen of the present invention are that it does notleak with changes in atmospheric temperature and pressure; it requiresno external devices for priming; it can be easily refilled withoutdisassembling; it is formed of a minimum number of pieces and may beassembled using a minimum number of steps; and it provides an easilyvisible level of the ink supply. In addition, the pen of the presentinvention provides a higher writing speed capability than heretoforeknown pens of comparable si'ze.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of oneembodiment of the pen of the present invention.

, FIG. 2 is an exploded perspective view of the pen illustrated in FIG.1.

FIG. 3 is a cross-sectional view of the pen taken along line 3-3 of FIG.2.

FIG. 4 is a cross-sectional view of the capillary passageway taken atthe section 4-4 in FIG. 3.

FIG. 5 is a partially cutaway perspective view of a second embodiment ofthe pen of the present invention.

FIG. 6 is an exploded perspective view of the pen illustrated in FIG. 5.

, FIG. 7 is a cross-sectional view of the pen taken along the line 7-7in FIG. 6.

rounds a cylindrical core 13-. The core 13 includes a writing tip 15integral therewith at one end and a square-thread, screw-like channel 17on the external lateral surface thereof. The sleeve 11 is dimensioned tobe pressed over the core 13 and form a tight fit therewith, thereby toclose,the open side of the screw-like channel 17 to form a continuouscapillary passageway. As viewed in FIG. 3, the right-hand end of thispassageway is vented to the atmosphere, and the left-hand end is coupledthrough a conduit 19 to the pen tip 15 which is press-fitted into a borein the end of core 13.

Both the core 13 and sleeve 11 are preferably formed of transparentplastic by an injection molding process. Core 13 has a central hollowportion 21 therein to reduce the bulk of the plastic material. Thisconfiguration minimizes internal stresses which might warp the core. Thesleeve 1 l is formed of transparent plastic to permit viewing of the inksupply.

The capillary serves as an ink reservoir and is filled by immersing oneend thereof into an ink bath and drawing a vacuum at the other end. Whenthe capillary is properly filled with ink so that no air bubbles aretrapped therein, the capillary passageway is both temperature andpressure stabilized, i.e., it will not leak with changes in atmospherepressure or ambient temperature. Leaking due to gravitational orinertial forces is prevented by the adhesion of ink to the capillarywalls and the surface tension of the ink-air interface at the pen tip.

When the pen is in contact with a sheet of paper, the force required todraw the ink from the capillary is derived from the capillary attractionforces between the ink and the paper cells contacted by the writing tip15. It has been found that the maximum velocity at which the pen willwrite and the volume of ink deposited on the paper is highly dependenton certain physical parameters of the pen. When the capillary forces arebalanced against gravitational forces, the following mathematicalexpression is obtained:

48, cos 0 (aghDl l/( r n) where S, is the surface tension of the ink-airfilm interface inside the capillary; 0 is the angle between the internalside wall of the capillary and a line tangent to the meniscus of the inkat the contact point of the ink and the side wall; 0- is the massdensity of the ink; g is the acceleration due to gravity; h is height ofthe fluid column (i.e., the effective fluid head); D, is the diameter ofthe pen tip opening; and D is the hydraulic diameter of the capillary,which in turn is given by the expression D (2ab)/(a+b) where a and b arethe dimensions shown in FIG. 4.

The pen parameters may be determined by first selecting the type ofmaterial from which the capillary walls are formed as well as type ofpen tip and ink to be used. This will fix the values of S,, a and D andwill permit a close approximation of the value of 0. The ink type andcapillary wall material should be chosen so that 0 is between 0 andi.e., so that the meniscus is concave. The value of g is a knownconstant. Thus,

the remaining terms h and 0,, may be selected to satisfy the aboveexpression. Satisfactory operation of the pen has been achieved with acapillary formed of a polycarbonate plastic material, and using acommercially available ink, such as that supplied by Graphic ControlsCorporation, Cherry Hill, N.J., under Part No. 8l-2- -0291-01. In thiscase, the effective head, h, was 1.67 inches, the pen tip diameter D was0.008 inch and the hydraulic diameter D was 0.025 inch, the latter ofwhich was obtained using the cross-sectional dimensions of a 0.017 inchand b 0.050 inch as shown in FIG. 4.

FIGS. 5-7 illustrate another embodiment of the pen. A rectangular-shapedpen body 23 is formed of transparent plastic by an injection moldingprocess, for example. One side of the block defines a rectangularlyaligned convolute channel 25 and a shallow cavity 27 connected by achannel 29 to the edge of the body 23. The other side of body 23 definesa convolute channel 31 which is rectangularly aligned with the axes ofthe longer portions of the channel perpendicular to those of channel 25.Channel 25 has one end 33 coupled through a conduit (not shown) in bodymember 23 to a pen tip 35 and the other end 37 coupled by a conduit 39through body member 23 (see FIG. 7) to one end of channel 31. The otherend of channel 31 is coupled by a conduit 41 through body member 23 tothe shallow cavity 27.

Two sheets of transparent plastic 43, 45 are ultrasonically welded onopposite sides of the plastic body 23, thereby closing the convolutechannels 25, 31 and the cavity 27. The capillary passageway thus formedis continuous and extends from the pen tip 35 through the entire lengthof convolute channel 25 orione side of body 23, then through the entirelength of convolute channel 31 on the other side of body 23 to thecavity 27 which is vented to the atmosphere through the short channel29. This long capillary passageway is filled with ink and serves as anink reservoir as described above.

The shallow cavity 27 on one side of body 23 serves as an internalpriming device. When the portion of the pressed at the same time thatthe vent conduit 29 is covered by the operators finger, air pressure iscreated at one end of the capillary passageway. Instead of manuallyclosing the vent, a one way valve (not shown). may be disposedin thevent conduit 29 to permit the entry but not the exit of airtherethrough. In either case, depression of the plastic sheet overcavity 27 will force ink to flow out of the pen tip, thus priming thepen for initial use or for additional use after a period of inactivity.

I claim: l. A compact, disposable writing unit for a graphical recordercomprising:

reservoir means defining a convolute capillary fluid passageway forcontaining an ink supply, said passageway having first and second ends,said first end being open to the atmosphere; a pen tip coupled in fluidcommunication with the second end of said passageway; said convolutecapillary passageway of said reservoir means being formed from a plasticblock and including:

a first portion disposed in a first plane, one end of said first portionbeing said first end open to the atmosphere;

at second portion disposed in a second plane parallel and adjacent tosaid first plane, one end of said second portion being said second endto which said pen tip is coupled; and

means for coupling said first and second portions in fluid communicationto provide a single continuous fluid path between said first open endand said pen tip; and

means for priming the writing unit to force ink to flow out of said pentip, said priming means including a manually deformable cavity having asingle inlet-outlet conduit coupled to said first open end of saidcapillary passageway, whereby said first open end may be closed and saidcavity com-.

pressedto force air under pressure into said capillary passageway,thereby to drive ink in said capillary passageway through said pen tip.

2. The device of claim 1, wherein said reservoir plastic sheet 43covering this cavity is manually de- 40 means is formed of opticallytransparent material,

thereby to permit viewing of t he ink supply.

3. The device of claim 1, wherein said deformable cavity is an integralpart of said reservoir means defining said first and second portions ofsaid convolute capillary passageway.

UNITED STATES PATENTTAND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,747,121".

DATED July 17, 19,73

|N\/,ENTOR(S) I Terry C. Siden ltis certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1, of the title page, after [76] Inventor: Terry C. Siden, 708Park Pl. Apt. 4,

Escondido, Calif. 92025" insert Assignee: Hewlett-Packard Company, PaloAlto, Calif.

Signed and Scaled this I sixteenth Day of March 1976 [SEAL] Arrest:

mu c. MASON c. MARSHALL DANN Arresting Officer Commissioner oflarenrsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION DATED 1 July 17, 1973 INVENTO 1 Terry C. Siden It iscertified that error appears in the above-identified patent and thatsaid Letters Patent a are hereby corrected as shown below:

Colunm l, of the title page, after "[76] Inventor: Terry C. Siden, 708Park Pl., Apt. 4,

Escondido, Calif. 92025" insert Assignee: Hewlett-Packard Company, PaloAlto, Calif.

Signed and Scaled this sixteenth Day of March 1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Attesting Officer Commissioner oj'Patentsand Trademarks Q

1. A compact, disposable writing unit for a graphical recordercomprising: reservoir means defining a convolute capillary fluidpassageway for containing an ink supply, said passageway having firstand second ends, said first end being open to the atmosphere; a pen tipcoupled in fluid communication with the second end of said passageway;said convolute capillary passageway of said reservoir means being formedfrom a plastic block and including: a first portion disposed in a firstplane, one end of said first portion being said first end open to theatmosphere; a second portion disposed in a second plane parallel andadjacent to said first plane, one end of said second portion being saidsecond end to which said pen tip is coupled; and means for coupling saidfirst and second portions in fluid communication to provide a singlecontinuous fluid path between said first open end and said pen tip; andmeans for priming the writing unit to force ink to flow out of said pentip, said priming means including a manually deformable cavity having asingle inlet-outlet conduit coupled to said first open end of saidcapillary passageway, whereby said first open end may be closed and saidcavity compressed to force air under pressure into said capillarypassageway, thereby to drive ink in said capillary passageway throughsaid pen tip.
 2. The device of claim 1, wherein said reservoir means isformed of optically transparent material, thereby to permit viewing ofthe ink supply.
 3. The device of claim 1, wherein said deformable cavityis an integral part of said reservoir means defining said first andsecond portions of said convolute capillary passageway.